(19) |
 |
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(11) |
EP 0 936 019 A3 |
(12) |
EUROPEAN PATENT APPLICATION |
(88) |
Date of publication A3: |
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21.03.2001 Bulletin 2001/12 |
(43) |
Date of publication A2: |
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18.08.1999 Bulletin 1999/33 |
(22) |
Date of filing: 12.02.1999 |
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(84) |
Designated Contracting States: |
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AT BE CH CY DE DK ES FI FR GB GR IE IT LI LU MC NL PT SE |
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Designated Extension States: |
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AL LT LV MK RO SI |
(30) |
Priority: |
17.02.1998 US 24944
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(71) |
Applicant: ILLINOIS TOOL WORKS INC. |
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Glenview, Illinois 60025 (US) |
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(72) |
Inventors: |
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- Hutchison, Richard
New London, Wisconsin 54961 (US)
- Uecker, James
Appleton, Wisconsin 54911 (US)
- Holverson, Todd
Appleton, Wisconsin 54914 (US)
|
(74) |
Representative: Rackham, Stephen Neil |
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GILL JENNINGS & EVERY, Broadgate House, 7 Eldon Street London EC2M 7LH London EC2M 7LH (GB) |
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(54) |
Method and apparatus for welding |
(57) A short circuit arc welding system has a control scheme uses a current command signal
to drive the output current. The command signal is comprised of a long-term current
command that sets the long-term current command level and a real time or short-by-short
current command. Arc voltage feedback is led to determine if the desired arc length
is present and to adjust the long-term command. The short-by-short current command
, derived from real-time arc current feedback and is used to control the burn-off
rate by an instantaneous, or short-by-short, adjustment of the current command. A
function of the time derivative of arc power, less the time derivative of arc current,
is used to detect, in real time, when the short is about to clear. A stop algorithm
is employed that monitors the arc on a short-by-short basis. When the process is ending
a very low current level is provided to avoid forming a ball. However, if a short
is created, Q
req after the low current level, a burst of energy is provided to clear or burn off the
short. After the short is cleared, very low current is again provided to avoid forming
a large ball. This is repeated until the wire stops and the process ends.